1. Field of the Invention
The present invention relates to a bill serial number reading device and bill serial number reading method for reading the serial number printed on a bill, and more particularly to a bill serial number reading device and method for reading the serial number of bills where the character color of the serial number and the background color thereof are different depending on the bill, and for still allowing extracting and recognizing the serial number when scribbling or contamination exists on part of the serial number or when a frame error occurs.
2. Description of the Related Art
When a serial number (predetermined digits of character information comprised of alphabets and numerics) printed on a bill is read, and generally the bill is transported, light is emitted to the portion where the serial number is printed, and the reflected light thereof is captured by an image sensor and the characters are recognized, but the serial numbers may or may not be read clearly depending on the color of the irradiation light source, color of the characters of the serial number, color of the background of the characters, and other factors.
For example, in the case of a Euro bill, the serial number overlaps with the background, and the character color and the background color of the serial number differs depending on the denomination, so if one type of LED light source is used as the irradiation light source, the scanned background differs depending on the denomination due to the relationship with the color of the irradiation light source in the binary data based on the image data acquired by scanning and reading the bill, which makes it difficult to clearly extract the serial number from the binary data.
FIG. 17 is a diagram depicting the relationship between the light source emission color, gray image, binary image and judgment result for a 20 Euro bill and a 50 Euro bill.
In this case, a green LED is used as a light source, so in the binary data based on the image data (gray image) acquired by scanning and reading each of the bills, the serial number (X001138509354) appears clearly in the 20 Euro bill, because the background is gray/blue, therefore the serial number can be accurately recognized based on this binary image data, but in the case of the 50 Euro bill, where the background color is brown, the serial number (V02382003184) cannot be accurately recognized because this background color remains and overlaps with the binary image of the serial number.
As a countermeasure to prevent the drop in the recognition rate of character recognition due to the difference of the background color, Japanese Patent Application Laid-Open No. 2002-185782 discloses a device and method for irradiating light with a same color as the half tone pattern of the background of a lottery number, and accurately reading only the character part (lottery number) using a drop out color method, which cancels the color of the half tone pattern section.
Therefore there is a conventional method of dropping out the background color and reading such information as a lottery number using the drop out color method, but if this known technology is applied to reading such bills as Euro bills, where the serial number and the background overlap and the character color and background color of the serial number differ depending on the denomination, a plurality of light sources which have different emission colors, depending on the bill, must be provided, which increases cost.
On the other hand, for such a bill depositing machine as an ATM which handles Euro bills, for example, some countries require by law that information on the individual who deposits the money and the serial number (predetermined digits of the character information comprised of alphabets and numerics) of the bill deposited by this individual are stored.
This is a measure for specifying the individual who deposited the money using the serial number of the bill as a key when the deposited bill is a problem bill, such as a stolen bill.
In the case of the bill serial number reading device for this type of system, the bill is transported, light is irradiated on the portion of the bill where the serial number is printed, and the reflected light thereof is captured by the image sensor, and the characters are recognized, as mentioned above.
In this serial number recognition, if scribbling or contamination exists on a part of the serial number of the bill, as shown in FIG. 18, for example, the binary image data of this part (numbers 2 and 3 of the lower left serial number in this example) becomes one block due to the above mentioned contamination, and this part may be recognized as one digit in error, although there are actually two digits.
In the case of a method of creating an extraction window to recognize the serial number of a bill, characters of all the digits of the serial number cannot be extracted if a frame error, where a part of the serial number extends outside the frame for reading, occurs.
In this kind of conventional bill serial number reading device, if scribbling or contamination exists in a part of the serial number of a bill or if a frame error occurs, it is generally judged that the number of digits of the serial number does not match with the number of digits of a serial number of this bill, and the recognition processing of the serial number is stopped.
Therefore if the serial number of a problem bill is notified to a financial institution and this serial number happens to be a serial number which could not be recognized for the above mentioned reason, the financial institution cannot specify the individual who deposited the money from the serial number, because this serial number is not stored.
In the field of character recognition, Japanese Patent Application Laid-Open No. 2-56688 discloses a technology of creating a density histogram from the variable-density image of the printed characters, determining the threshold value from the shape of the density histogram, executing binary processing, and extracting characters, so that the desired characters are accurately detected even if density unevenness and noise are included in the background area, and each one of the detected characters becomes a binary image free of noise and character deformation.
This known technology, however, is focused on improving the accuracy of character recognition, and is not practical to meet the demand for the above mentioned system, which is recognizing the serial number accurately enough to specify the individual who deposited the money, since the processing is complicated and the processing time is lengthy.
Therefore, in the case of a conventional bill serial number reading device used for a system which stores information on an individual who deposits money and the serial number when the bill is deposited, and later specifies the individual who deposited the money by the serial number, if scribbling or contamination exists on a part of the serial number of the bill or if a frame error occurs, it is judged that the number of digits of a serial number does not match with the number of digits of the serial number of this bill, and the recognition processing of this serial number is stopped, so if this serial number which could not be recognized is the serial number of a problem bill, the financial institution cannot specify the individual who deposited the money from the serial number of the problem bill, because this serial number is not stored.